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Volume 32, Number 9—September 2026

Research

Improved Case Detection of Fleaborne Typhus by PCR Testing, Los Angeles County, California, USA, 2022–2024

Armine Sanosyan, Zuelma A. Contreras, Van Ngo, Michael K. Brown, Nicole M. Green, Lee A. Borenstein, Jill K. Hacker, Will S. Probert, Alexa C. Quintana, Monica P. Haw, and Umme-Aiman Halai
Author affiliation: Los Angeles County Department of Public Health, Los Angeles, California, USA (A. Sanosyan, Z.A. Contreras, V. Ngo, M.K. Brown, N.M. Green, L.A. Borenstein, U.-A. Halai); California Department of Public Health Center for Laboratory Sciences Viral and Rickettsial Disease Laboratory, Richmond, California, USA (J.K. Hacker, W.S. Probert, A.C. Quintana, M.P. Haw).

Main Article

Table 2

Results of additional testing for initial 114 Rickettsia typhi low-titer positive serum specimens, Los Angeles County, California, USA, 2022–2024*

Category No. (%) specimens
Initial commercial laboratory IFA R.typhi IgG titer
<1:64 58 (51)
1:64
 56 (49)
Initial commercial laboratory IFA R. typhi IgM titer
<1:64 21 (18)
1:64 65 (57)
1:128
 28 (25)
Repeat R. typhi IFA IgG titer
<1:64 14 (12)
1:64 20 (18)
1:128 35 (31)
1:256 18 (16)
>1:512 25 (22)
Not done or unspecified 2 (2)
Total with IgG that met laboratory criteria (>1:128)
 78 (68)
Repeat R. typhi IFA IgM titer
<1:64 18 (16)
1:64 6 (5)
1:128 24 (21)
1:256 24 (21)
>1:512 38 (33)
Not done or unspecified 4 (4)
Total with IgM that met laboratory criteria (>1:256)
 62 (54)
IFA serologic testing results higher upon repeat testing 106 (93)
IFA serologic testing results met laboratory criteria† upon repeat testing
95 (83)
PCR results
Positive 81 (71)
Negative 22 (19)
Unsatisfactory or indeterminate 10 (9)
Not tested
 1 (0.9)
Case classification change
CDPH suspected to probable 32 (28)
CDPH suspected to confirmed 81 (71)
No change 1 (0.9)

*CDPH, California Department of Public Health; IFA, immunofluorescence assay. †IgG titer >1:128 or IgM titer >1:256.

Main Article

Page created: July 17, 2026
Page updated: August 12, 2026
Page reviewed: August 12, 2026
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